Travelling grate shale retorting



Dec. 9, 1969 J. H. HADDAD ETAL 3,483,115

TRAVELLING GRATE SHALE RETORTING Filed April 15, 1966 //2 1/6/7 forsJames H Hack/0d United States Patent US. Cl. 208-11 5 Claims ABSTRACT OFTHE DISCLOSURE A method of retorting oil shale in a horizontally movingbed wherein gaseous material flowing transversely through the shale bed,all in a downflow direction through a plurality of gas contacting zonesestablishes a restricted kerogen decomposition heat front in the top ofthe bed and drives the decomposition heat front progressively downwardlyas the bed moves horizontally through the retorting section. Gaseousmaterial obtained from an intermediate portion of the shale bed, fromwhich oil mist was recovered, is employed to effect partial cooling ofgaseous material recovered from a latter portion of the shale bed. Thiscooled gas is introduced to an initial portion of the shale bed tocondense out entrained oil constituents and to preheat the shale.

This invention relates to an improved method for retorting oil shale torecover shale oil. More particularly, the present invention relates tothe method and combination of process steps for retorting oil bearingshale in a horizontally moving bed.

Shale oil technology as we know it today has not reached an advancedcommercially attractive stage and considerable work is yet to be done indeveloping systems having commercial acceptance for an economic recoveryof valuable oil products. Oil shale is known as a sedimentary rock whichcontains a solid organic material known as kerogen. When this oil shaleis heated to a suitable elevated temperature, the kerogen is decomposedby pyrolysis to shale oil, gas and a carbonaceous residue.

At the present time, a great number of shale oil retorting processes areavailable. Each of these processes are undesirable in at least one majorrespect which greatly reduces the economic incentive for theircommerical application. Some of the major problems in shale retortinglay in controlling shale bed temperature, shale retorting time and otfgas temperature in a manner to maximize shale oil yield.

In shale retorting, large quantities of heat must be supplied to theshale bed to eifect substantially complete kerogen decomposition. Theheat is supplied by a variety of methods including burning a portion ofthe shale off vapor or by burning the kerogen or organic carbon in aportion of the shale bed. In any event, the heat is usually passedthrough the shale bed by using very large quantities of gas. The desiredhydrocarbon products produced by kerogen decomposition are vaporized,carried out of the bed by the gas moving through the bed and recoveredfrom the otf gas. Since very large quantities of gas are employed, it isdesirable that the olf-gas temperatures be sufficiently low tofacilitate oil recovery. The alternative of cooling hot off-gas by heatexchange is not attractive due to the very large amount of necessaryheat exchange surface and the problems associated with coking of hot-gasconduits and exchangers. The duel requirements placed upon the gas of(1) supplying sufiicient heat to the shale to eifect kerogendecomposition and (2) being of a sufficiently low temperature upon exitfrom the shale to facilitate oil recovery have resulted in retortoperational problems which have not been satisfactorily solved by theprior art.

These problems are complicated by the presence of fines within the shalebed. To satisfactorily retort shale, it is necessary that the shale bein relatively small particle form to effect desirable heat transfer andto obtain high yields of shale oil. The most common method of formingrelatively small shale particles is by crushing. When the shaleparticles are crushed there is a wide variance in particle size from alarge quantity of fines which are particles less than A inch in size areformed. For example, where it is desirable to obtain shale particleswhich have a maximum size of 4 inches by present crushing methods, thequantity of fines produced will vary from a minimum of about 8 percentto 30 percent by weight depending on the types of crushers used. Underretorting conditions of high gas rates and high temperatures, the fineswill reflux between the cool and hot portions of the bed in many of thepresently known processes. For example, in shaft-furnace type retortswhere the shale moves downwardly through the retort by gravity and thegas flows upward through the retort countercurrent to the shale flow,the oil vapors condense on and entrain the fines in the cooler upperlevels of the bed and when refluxed to the hot lower portion of the bedwill coke thereon. This results in an oil yield loss. Another result isthe bridging of the particulate shale within the bed. Gadually theamount of fines and coke builds up in the bed and clinkers form. Thisresults in additional restricted movement of shale particles through theretort. This condition is prevalent in the above-described shaft furnacetype of retort even though the raw shale fines formed in the crushingoperation are removed from the shale inventory prior to charging to thefurnace. It has been found that the spent shale from these furnaces,even when operating with a fines-free raw shale charge, contains finesconcentrations higher than 15-20 percent. These fines are formed duringthe heating and retort process due to weakening of the shale structure.

In addition, concentrated fines cause undesirable gas channeling throughthe shale bed. This results in nonuniform heating of the shale bed andfurther oil yield losses to coke. In addition, fines refluxing whichcauses fines buildup in the bed can result in undesirably high pressuredrop throughout the bed. Further, the refluxed fines are subjected toexcessive heating which results in carbonate decomposition. Whenexcessive carbonate decomposition occurs, the amount of heat availablefor kerogen decomposition is decreased since carbonate decomposition isan endothermic reaction. The gross process heat requirements for kerogendecomposition then correspondingly increase.

An object of the present invention is to provide an improved oil shaleretorting process which is thermally eflicient.

A further object of the present invention is to provide a shaleretorting process which minimizes undesirable shale fines formation andrefluxing or fines buildup in the shale retorting section.

A still further object of the present invention is to retort oil shalein a horizontally moving bed in a manner which more efiiciently utilizesheat carrying gasiform material to effect kerogen decomposition andrecovery of oil from the shale bed.

A still further object of this invention is to provide a method foreificiently retorting the raw shale fines which are produced during thecrushing step.

Other objects and advantages of the present invention will become moreapparent from the following description.

Accordingly, the present invention relates to the method and sequence ofprocessing steps for decomposing shale kerogen in a horizontally movingbed of shale with heat carrying gasiform material caused to move in acontrolled and restricted manner through the shale bed. That is,gasiform material is employed to form a heat wave at kerogendecomposition temperature either on an upper or lower portion of the bedsurface. In addition, the gasiform material is employed to move the heatwave progressively through the vertical height of the bed. The heat wavedepth forms only a relatively narrow portion of the bed vertical heightin any given bed section. In cross sectional representation, the heatwave appears to slope vertically away from the bed surface where gas isintroduced to the bed and horizontally in the direction of the shale bedoutlet. When the heat wave has passed through the entire bed height,substantially all of the kerogen in the shale bed has been decomposed toselectively produce oil product in high yields.

In accordance with the present invention, a bed of particulate shale ofdesired thickness or height is laid down on a traveling grate whichmoves horizontally and sequentially through a plurality of gascontacting zones. In the retorting operation, a heat wave carried by hotgasiform material and having a temperature sufiiciently elevated toeffect kerogen decomposition is initiated on a portion of either theupper or lower surface of the shale bed as it moves horizontally intothe retorting section. As the shale bed moves in its horizontal path, itis continuously subjected to contact with gasiform material which iscaused to move through the shale bed thereby moving the kerogendecomposition heat wave in the form of a continuous relatively narrowband through the entire bed vertical height. The incoming gas isintroduced in all contact zones on the same horizontal level of the bedwhere the heat wave is initiated. In the process of this invention, gasflow throughout the horizontally moving bed height can be either alldownfiow or upflow. and one important aspect of the method and system ofthis invention is directed to maintaining the flow of gas all in thesame direction for reasons herein described.

The gas inlet temperatures and gas flow rates to various horizontalareas of the bed from the shale inlet to the spent shale outlet may bevaried and maintained in a manner to move the previously generated heatwave through the entire vertical height of the bed while at the sametime cooling the spent shale as the bed progresses horizontally throughthe retort. The gas inlet temperatures and gas flow rates depend in partupon the shale particle size in the bed and the shale mass flowratethrough the retort but in any event are regulated to obtain thedesired kerogen decomposition heat wave progression through the bed. Theheat wave in a given section of the retort is of sufiicient magnitude toeffect substantial decomposition of the kerogen in a portion of theshale bed without effecting substantial overcracking of the kerogendecomposition product comprising oil vapors. The vapor outlettemperature of various sections of the retort are maintainedsufficiently low to avoid substantial conversion of oil vapors to cokeand to effect more efficient removal and recovery of oil productstherefrom. Further, the vapor outlet temperatures from the various bedareas are maintained to effect a more desirable temperature and heatingprofile throughout the bed of shale and more efiicient utilization ofavailable heat in the process.

Hereinafter, for purposes of convenience the process and system of thisinvention will be described in terms of an operation wherein alldownfiow of gas is used. However, it is to be clearly understood thatall upfiow can also be employed even though it is preferred to use alldownfiow of gas through the shale bed. In the method and system of thisinvention, heat is supplied to a portion of the top of the horizontallymoving shale bed to provide an initial heat wave having temperatures inthe range of from about 1100 F. to about 1500 F. For purposes ofconvenience in controlling gas flow and temperature profile in the shalebed, it is preferred to introduce the hot gaseous material through aplurality of adjacent gas distributor means positioned throughout aportion of the length and at substantially the upper surface of the bedof shale. The thus distributed hot gaseous material causes a heat zoneor band wherein kerogen decomposition takes place. Subsequent flow ofcolder recycle gases to the surface of the shale bed downstream from thehot gas inlet areas causes the hot band to move downwardly through thebed of shale as the bed moves horizontally through the retort thuscausing a significant change in the bed vertical temperature profile. Abed in vertical cross-section view along its length would show a heatwave front wherein kerogen decomposition takes place sloping downwardlyin the direction of the spent shale outlet. In the method of thisinvention the bed becomes gradually hotter in the lower portion of thebed while the upper portion of the bed becomes gradually cooler as thebed moves horizontally through the shale retort section. The incomingrecycle gas to each retorting section removes heat from the top portionof the bed and releases the heat in a lower portion of the bed. The heatgenerated and/or picked up and carried by the gas from the hot retortedshale and subsequently released to colder raw shale below has been foundto be sufiicient to maintain the heat wave above described and effectkerogen decomposition of the shale as the heat wave moves continuouslydownwardly through the bed. Thus the recycled gases cause the kerogendecomposition heat wave to move progressively downward through theentire vertical bed height as the bed moves horizontally through theretorting section.

Substantially downstream of the shale inlet and initial decomposition ofoil shale, a relatively cool recycle gas from which condensible oilproducts have been removed is introduced to the top of the shale bed forflow downwardly therethrough. In this downstream portion of the bed, thekerogen decomposition heat wave is located in the lower portion of thebed. The incoming relatively cool gas is heated by the residual heatremaining in the shale in the upper portion of the bed and this heat iscarried downwardly by the heated gas for release in a lower bed sectionto provide kerogen decomposition temperatures. The outlet gastemperature in the downstream portion of the bed is substantially higherthan the outlet gas temperatures in the initial portions of the bedsince the amount of cool shale underlying the kerogen decomposition heatwave diminishes as the bed moves horizontally through the retort.Therefore, a progressively smaller portion of the bed is available toextract heat from the vaporous material coming from the kerogendecomposition section of the shale bed. Therefore, in this portion ofthe retort, it is important to maintain close temperature contacts toavoid undesired cracking and heat damage to the horizontally moving gridsupporting the shale bed and other related equipment.

It is clearly evident from the above that a continuous heat wave atkerogen decomposition temperatures is formed and maintained whichappears in cross section to slope downwardly in the direction of thehorizontal shale movement from the top of the bed to the bottom of thebed. Thus the bed temperature above and below the established heat Waveand kerogen decomposition portions of the bed will be below the heatwave temperature by virtue of the recycle gas and the shale bed not yetheated to the desired elevated temperature. Thus, advantage is taken ofthe vertical temperature profile in various portions of the bed torecover kerogen decomposition products and heat recycle gas moreefiiciently. That is, when gas is introduced into the shale bed, afterthe heat wave is established, the bed gives up heat to the gas above thekerogen decomposition band but recovers heat from vaporous materialbelow the band. In this manner, the bed erves as a most efificient heatexchange means to assist in effecting kerogen decomposition and recoveryof condensible products from the vaporous material leaving the kerogendecomposition heat wave band. Further, when the heat Wave reaches thebottom of the retort, the bed is cooled to a sufficiently low averagetemperature that it can be removed from the retort without presentingunusual handling problems and without need for special heat resistantapparatus.

A further advantage is derived by the method and process of thisinvention in respect to problems associated with the presence of shalefines. In the present process solid particles fines refluxing andbuildup is avoided because the gas flow through the bed is all in thesame direction. The large majority of the fines remain entrapped in thevoids between the large shale particles. However, a small portion of thefines are entrained in the moving gas. In the method of this invention,a wetted wave front containing partially condensed oil vapor obtainedfrom kerogen decomposition precedes the heat wave in its verticalmovement through the bed. This wetted wave front in the bed tends totrap those fines carried by the gas. The wetted wave front is formed byoil condensation on the shale particles in the relatively cool portionof the bed located below the kerogen decomposition heat wave. Thecondensed oil then removes the fines from the gas. As the heat waveprogresses downwardly, the great majority of the condensed oil isrevaporized and directed to a lower portion of the bed. A small portionof the condensed oil is converted to coke with the fines being retainedin the formed coke. The downwardly moving oil is condensed andrevaporized as described above and eventually is removed in the form ofa mist from the bed. The amount of coke formed in the bed is relativelysmall and is distributed over a large surface provided by the shaleparticles.

Oil containing gases are removed at spaced intervals from the bottomportion of the bed of shale moving through the retort section atsubstantially different temperature levels in a plurality of separategas recovery zones. Each gas recovery zone is associated with aparticular oil separation step to which the recovered gases are directedfor separation of oil therefrom. Generally, the average gas temperaturein each recovery zone will be progressively higher in that portion ofthe shale bed wherein the kerogen decomposition heat wave is nearest thebed outlets. Advantage is taken of these varying temperature conditionsto recover condensibles and condensed oil from the gasiform streamsemployed in the process and to heat and cool shale particles. Thus, thegases are sequentially subjected to a plurality of oil separation stepsby passage through the shale bed in a manner that takes advantage of thetemperature profile in any particular portion of the moving shale bed.

The oil recovered at higher temperatures is recovered in oil separationsteps associated with those high temperature gas recovery zones so thatsubstantially only the middle and/or higher boiling portions of theshale oil are recovered therefrom initially. The gases and uncondensedvapors are thereafter directed to that portion of the shale bed of lowertemperature to affect a further cooling of the gases and vapors andrecovery of condensible material therefrom. This usually comprises theinitial portion of the bed nearest the shale inlet point.Simultaneously, in the initial portion of the bed the gases anduncondensed vapors are cooled and the bed is preheated. The reducedvapor temperatures in this portion of the shale bed cause the lowerboiling fraction of the shale oil therein to condense. The condensed oilis recovered in the oil separation step associated therewith. In thismanner, substantially all of the vaporous shale oil is recovered. Inaddition, it is unnecessary to provide an additional heat exchange stepto recover substantially all of the shale oil from the bed off gas.Further, the heat removed from the shale bed by the off-gas and vaporsin the downstream portion of the bed is substantially recovered in theinitial portion of the shale bed thus adding to the thermal efficiencyof the process.

In the process of this invention, a plurality of gas recovery zones areemployed. For example, when only two gas recovery zones are employed,the first zone extends in the direction of shale movement from the shaleinlet to that point of the bed wherein the heat wave is initiated. Thesecond zone extends through the remaining horizontal bed length whereinoil containing vapors are emitted from the bed. The condensed oil in thegases from the second zone are removed from the gas in an oil separationstep associated therewith. The gas and remainder of the uncondensedvapors are then recycled to the top of the bed in the first zone andpassed there through to cool the same. The gases and condensed oil inthe form of mist from the first zone are recovered and directed to anoil separation step different from the oil separation step associatedwith the second recovery zone to separately recover relatively lowboiling shale oil from the gas. A portion of the gas from the first zoneis then vented, while the remainder is directed to the portion of thetop of the bed associated with the second gas recovery zone. The vapordirected to the top of the bed above the second recovery zone is splitinto at least two streams and is introduced in at least two separate bedsections. In the first section above the second recovery zone nearestthe shale inlet, a heat wave having kerogen decomposition temperature isinitiated on top of the bed. The heat can be supplied as for example byintroducing air and fuel at combustion temperature to the top of thebed; burning a portion of the recycled vapors; by burning a portion ofthe kerogen in the shale bed or by a combination of these methods. Inthe second section on top of the bed associated with the second gasrecovery zone, the gases from the first zone are introduced withoutadditional heating or cooling thereof.

In another embodiment of the present invention, the recovery of oil fromthe shale bed can be effected in three main zones. The first recoveryzone extends horizontally in the direction of shale movement from aboutthe shale inlet to about that point of the bed wherein the heat wave isinitiated. The second recovery zone corresponds to that portion of thehorizontal bed wherein the heat wave is initiated and maintained at ornear the top surface of the bed. The third recovery zone corresponds tothat top portion of the horizontal bed wherein gases from the first zoneare introduced without an intermediate gas heating or cooling step. Thegases from the second and third vapor recovery zones are each directedto a separate oil recovery step. The gases and any uncondensed vaporsfrom each of the oil recovery steps are directed to the top of the firstzone to pass downwardly therethrough. The gases are cooled and vaporscooled and condensed while the bed is preheated in the first zone. Theeifluent gases from the first zone are directed to an oil separationstep associated therewith to remove the condensed shale oil from thegases obtained from the second and third oil separation zones. A portionof the first zone gases are vented. The remainder of the first zonegases are directed to the top of the second and third zones inrespective amounts to maintain the desired heat wave progression throughthe bed vertical height.

In a preferred embodiment of the present invention the recovery of oilfrom the bed is conducted in three main zones. The three gas recoveryzones are arranged as described above. The difference between thisembodiment and that described above wherein three recovery zones areemployed is the flow of gas from the second zone. In this embodiment,the off gas from the second zone is directed to the oil recovery stepassociated therewith. The gas from the recovery step is then directed tothe third gas recovery zone prior to being recycled to the top of thefirst zone. In this manner, the off gases and vapor in the third zoneare cooled prior to being subjected to an oil recovery step. Even thoughthis cooling of the third zone off gas and vapor is obtained at theexpense of heating the second zone oif gas, certain advantages aregained. The third zone ofi gas temperature is higher than the precedingtwo zones. Thus the gas contains higher boiling oil fractions which havea greater tendency to coke as compared to the lower boiling fractions.It is therefore desirable to quickly reduce this gas temperature beforecoke formation begins. In the alternative embodiment having three offgas zones described above, it is also possible to obtain desired low otfgas temperatures in the third zone without an additional heat exchangestep. However, this is accomplished by using a bed having a horizontallength longer than theoretically necessary to obtain a complete kerogendecomposition. In the additional portion of the third zone after thekerogen decomposition has reached the bottom of the bed, graduallycooler vapor is passed therethrough. Thus, this cool gas mixes with thehot gas to lower the average gas temperature.

As discussed above, it is desirable to maintain the off-gas temperaturein each recovery zone as low as possible while still effectingrelatively complete kerogen decomposition in the bed. When two gasrecovery zones are employed, the gas in the first gas recovery zoneassociated with the bed preheating zone should be maintained below about150 F., while the gas in the second gas recovery zone associated withthe retorting zone should be maintained below about 500 F. When three ormore gas temperature in all the recovery zones are maintained tain theaverage gas temperature in the first gas recovery zone associated withthe bed preheating zone below about 150 F., the gas in the last gasrecovery zone associated with the last portion of the retorting zonebelow about 500 F. and the gas in at least one intermediate gas recoveryzone below about 350 F. In any event, the gas temperature in all therecovery zone are maintained below about 500 F. to reduce cokeformation. The average shale temperature at the retort outlet ismaintained below that temperature will either thermally degrade thedischarge apparatus or support. combustion of carbonaceous residue inthe shale. In the process of this invention, this average shale outlettemperature is preferably maintained below about 400 F.

The figure represents in cross section the embodiment of this inventionwherein three gas recovery zones are employed and gases from the secondand third zones are mixed prior to being directed to the first zone.

Particulate shale which has been ground to a target average size ofabout 0.75 inch with a maximum particle size of about 4 inches isintroduced into a hopper 1. The shale is directed from hopper 1 toclassifier 3 through conduits 4 and 5. In classifier 3, the shaleparticles are classified according to size with the larger particlesbeing directed to the bottom of the bed and the fines being directed tothe top of the bed. Seal gas is introduced into conduits 4 and 5 toprevent air from entering the shale bed. In this embodiment, a doubleseal gas system is employed in conduits 4 and 5. The two seal gas flowrates are controlled so that the differential pressure between the twoseal gas inlets 6 and 7 is essentially zero. The shale is introduced ata rate so that a relatively thick bed is formed on a horizontally movingperforated grate 8. The bed thickness on the grate 8 is maintained atabout 6 feet. The small amount of fines which sift through the bed arerecovered in hopper 9 and recycled through conduit 10 to the shale inlethopper 1. The moving grate 8 causes the shale bed thereon to progresssequentially through zones 11, 12 and 13. The uncondensed gas from zones12 and 13 are recycled to gas plenum 14 on top of the bed in zone 11through conduits 15, 16 and 17. The uncondensed gas passes downwardlythrough zone 11 through the grate 8 and into a gas recovery zone 18located below the grate 8. The gas in gas recovery zone 18 is maintainedat a temperature below about 130 F. At this temperature, most of theshale oil is in the form of a condensed mist. The condensate andremaining gas are directed to an oil recovery step 19 through conduit20. Oil recovery step 19 can be, for example, a cyclone separator or anelectrostatic precipitator. Condensed oil obtained from oil recoverystep 19 is directed through conduit 21 to storage not shown.

Uncondensed gas from recovery zone 19 is directed through conduits 22,23, 24 and 25 to the top of the shale bed in zones 12 and 13. Theuncondensed gas to zone 12 is first introduced into plenum chambers 26and 27. Air is introduced to plenum chambers 26 and 27 through conduits28 and 29. At start up, a fuel can be introduced to plenum chamber 26through conduit 30 to a-dmix with the air and recycled uncondensed vaporunder conditions to cause combustion in plenum 26. After start up it isusually unnecessary to add fuel to maintain combustion in plenum 26. Inplenum 227, a portion of the uncondensed gas is burned. The resultantheat from the combustion in these two plenums is absorbed by the shalebed directly underneath these zones. By this heating, a heat wave atkerogen decomposition temperature is initiated on top of the bed in zone12.

The kerogen decomposition zone is caused to move downwardly and towardthe shale outlet in a configuration shown in FIGURE 1. Representativetemperatures of the gas introduced to each zone as well as the bedtemperature profile is shown in FIGURE 1. The ratio of gas rate to theshale rate in each zone is adjusted to provide the representativetemperature profiles shown. The gas in vapor zone 12 is caused to movedownwardly through the entire vertical height of the bed. This gas isrecovered in plenum zone 35 at a temperature below about 225 F. At thistemperature a major portion of the oil has condensed. The uncondensedand condensed oil and gas are directed through conduit 36 to an oilseparator 37 wherein oil is recovered through conduit 28 and uncondensedvapor and gas are directed to plenum chamber 39 through conduit 40.

In zone 13, recycled gas from oil recovery step 19 is introduced intoplenum chamber 41 on top of the bed at a temperature of about F. Thisgas is acused to move downwardly through the entire vertical height ofthe shale bed. In so doing, the top portion of the bed is cooled whilethe bottom portion of the bed is progressively heated until the kerogendecomposition heat wave reaches the grate 8. That portion of the bedlying between this point and the shale outlet in a horizontal directionis cooled through the entire vertical height. The off-gas from zone 13is recovered in plenum chamber 39 at a temperature, when admixed withthe uncondensed vapor from oil recovery step 31, of below about 400 F.At this temperature an additional portion of the higher boiling fractionof the shale oil is condensed. The uncondensed and condensed shale oiland gas is directed from plenum chamber 39 through conduit 42 to oilrecovery step 43 wherein shale oil is recovered. The uncondensed vaporand gas from oil recovery step 43 is directed through conduits 44, 15,16 and 17 to the top of zone 11 into the plenum chamber 14. The gas inplenum chamber 14 is caused to move through the vertical height of thebed in zone 11 in a manner described above. Blowers are provided in thevarious gas conduits to ensure gas flow downwardly through the bed. Thegas flow rates to plenums 14, 27 and 41 are maintained respectively atabout .765 ton vapor/ tons shale, .447 ton vapor/ tons shale and .483ton vapor/ tons shale.

The grate 8', after progressing through zone 13 is contacted with asmall portion of gas introduced through conduit 45 which removes anycoke which has formed in the perforations of the grate. This gas movesonly through a very small portion of the vertical height and isrecovered in plenum chamber 39. The grate 8 is in sections and abovehopper 47 the sections are tipped so that the shale thereon can beremoved. The shale is broken up by the clinker breaker 46 and thereaftermoves by gravity to hopper 47 and directed outwardly from the retortzone through conduit 48 onto a conveyor 49. Conduit 48 is sealed fromthe atmosphere by a dual-gas seal system by the introduction of seal gasthrough conduits 50 and 51 similar to that described above for the inletseal system. The relative sizes of the gas inlet plenums areapproximately proportional to the inlet gas flow rates thereto. Toafford relatively complete clearing of the grate 8, it is subjected to ajet of fluid and/ or solids through conduit 52. The material entrainedon the grate is directed to hopper 53.

In the process of this invention, the shale bed can be moved in a closedhorizontal path as for example in a circular path or in an openhorizontal path as for example in a straight line. In any event, theshale bed is continuously moved through a plurality of vapor contactzones. The vapors in each zone are introduced at a pressure sufficientto ensure vapor How in one direction through the bed vertical height.The gas pressure differential between the top and bottom of the bed toensure this flow depends upon a number of factors including the averageshale particle size, bed thickness, the gas flow rate used, and thetemperature conditions of the bed. In the process of this invention, theaverage shale particle size is maintained below about 2 inches andpreferably below about 0.6 inch. The shale bed thickness is maintainedbelow about 15 feet and preferably between about 4 feet and about 8feet.

In operation, the particulate shale can be directed onto the gratethrough a feeding device which stratifies the shale according to sizewith larger shale particles being located on the grate and the finesbeing located on top of the bed. In one embodiment of this invention,means can be provided below the bed and preceding the first vaporrecovery zone to recycle the small portion of the fines sifting throughthe bed back to the top of the bed. The stationary gas plenum chambersabove and below the moving retort are sealed from the atmosphere as forexample by a liquid seal to contain the gases. The moving grate movesthe shale bed serially through the gas con tact zones to effect completekerogen decomposition. The temperature profile of the spent shale upondischarge from the grate may vary from about 150 F. at the top of thebed to as high as about 600 F. at the bottom of the bed. The spent shaleis removed from the grate and directed to spent shale container whereinthe shale is mixed and the temperature of the individual particlesallowed to equilibrate by conductive heat transfer to reduce maximumparticle temperature below 400 F. maximums. To assist removal of spentshale for the grate, apparatus can be used to break up the shale bed toassist in shale movement to storage. The spent shale container is alsosealed from the atmosphere but is open to the retort vapors. The coolspent shale is removed from the container and disposed of. The movinggrate is then directed to the shale inlet portion of the retort whereinfresh shale is introduced. After spent shale is removed from the grateand prior to introducing fresh shale thereon, any coke and/orparticulate shale in the grate perforation is removed therefrom as forexample with high velocity jet cleaning or by burning.

The vapors directed to each zone are first directed to inlet plenumchambers adjacent the bed. These inlet plenums operate to separate thevapors so that different conditions of vapor temperature and vapor flowcan be maintained in various portions of the bed. In addition, the vaporinlet plenums provide relatively uniform vapor flow through the verticalheight of a given portion of the shale bed. Each of the plenums can besubdivided into smaller chambers to provide more efficient vapor flowcontrol. Similarly, the vapor outlet plenums can be subdivided intosmaller chambers to improve vapor flow control. Compressors are providedin various vapor lines as needed to maintain the desired pressuregradient through the shale bed.

We claim:

1. A method for thermally decomposing a relatively deep bed of oilyielding granular material which comprises moving a bed of oil yieldinggranular material horizontally through a confined passageway under atemperature profile provided to raise the temperature of the bed to anoil yielding decomposition temperature followed by cooling of the oildepleted bed with gaseous materials of selected temperature conditionsbeing flowed generally downwardly through said horizontaly moving bed,the preheating of said shale bed being initiated with partially cooledoil rich gaseous material hereinafter recovered at an elevatedtemperature from the bottom of the bed adjacent the end of itshorizontal travel and cooling of the bed after removal of oil beingparticularly accomplished with oil lean gaseous material recovered fromthe bottom initial portion of said horizontally moving bed, gaseousmaterial temperatures suitable for effecting thermal separation of oilcomponent from the granular material being obtained by burning a portionof the separated oil lean gaseous material external to said bed andthereafter introducing the hot gaseous material thus formed to the topof said bed in a restricted area down stream of the inlet of the bed tothe confined passageway, causing the thermal oil separation temperatureprofile to progress generally downwardly through said horizontallymoving bed by the oil lean gaseous material thereafter passed downwardlythrough said bed and employing gaseous material removed from the bottomintermediate portion of the bed to partially cool oil rich gaseousmaterial recovered from a latter portion of the bed for recycle to theinitial preheat portion of the bed as above described.

2. A method for retorting a bed of oil shale particulate movinghorizontally through a confined passageway which comprises establishinga restricted kerogen decomposition heat front area with hot gaseousmaterial in the top of said bed adjacent the inlet thereof to theconfined passageway, driving said kerogen decomposition heat frontprogressively downwardly through said horizontally moving bed withhereinafter obtained cooled gaseous material obtained from the initialportion of said bed introduced to said bed downstream of said heat frontarea to cool the kerogen depleted shale, recovering gasiform productmaterial of increasing temperature in the direction of the bed flow fromthe bottom of said bed in a plurality of separate gas recovery zones,separating oil constituents from gaseous .material recovered from eachof the gas recovery zones, effecting cooling of the highest temperatureseparated gasiform material with cool gaseous material recovered from anupstream portion of the shale bed and employing separated gaseousmaterial of relatively high and low temperature after removal of oilconstituents to maintain the desired temperature profile of said shalebed.

3. A process for retorting oil shale particles which comprises moving abed of shale particles horizontally through a confined passagewayprovided with a plurality of gaseous material distributing sections onone side of said horizontally moving bed opposite to gasiform materialcollecting sections, causing gaseous material at preselected temperatureconditions to move through said horizontally moving shale bed throughoutthe length thereof from said distributing to said collecting sections,employing gaseous material recovered at an elevated temperature from anintermediate section of said horizontally moving bed to effect partialcooling of higher temperature gaseous material recovered from adownstream portion of said shale bed to permit recovery of oilyconstituents therefrom, employing hot gaseous material recovered fromthe downstream portion of said shale bed after partially cooling asabove described to give up heat to the bed of shale introduced in aninitial portion of said confined passageway, initiating a kerogendecomposing heat front on the surface of said horizontally moving shalebed downstream of the shale preheating region, employing cooled gaseousmaterial recovered from said shale preheating region to drive saidkerogen decomposing heat front through said shale bed while effecting asimultaneous cooling of the kerogen depleted oil shale through which thegaseous material flows, separating retorted oil constituents fromgaseous material streams of different temperature levels recovered fromthe shale in said confined passageway in a plurality of separation zonespermitting the recovery of at least two separate gas streams ofsignificantly different temperatures for use in the process as abovedescribed.

4. A method for retorting oil shale particles which comprises causing arelatively deep bed of said shale particles of varying temperatureprofile caused by the flow of gaseous material therethrough to movehorizontally through a confined passageway generally transversely to thedownfiow of the gaseous material, accumulating separate gasiformmaterial streams varying considerably in temperature from the bottom ofthe shale bed in a plurality of at least three separate gasiformmaterial collecting chambers, said collected gasiform material streamincreasing in temperature in the direction of shale flow, separating oilmist from gaseous material in each of said collected gasiform streams atdifferent temperature conditions, employing gaseous material of reducedoil content and obtained from an intermediate portion of said horizontalbed to effect a partial cooling of the highest temperature gasiformmaterial recovered from a downstream portion of the shale bed wherebyoil constituents are separated from the highest temperature material,employing elevated temperature gaseous material of reduced oil contentthus recovered from a downstream portion of the shale bed to preheat theshale and con dense out entrained oil constituents on the shale thuscontacted in the initial portion of the confined passageway, passing aportion of relatively cool gaseous material freed of oil constituentremoved from the initial portion of the shale bed through a combustionsection to establish a high temperature gaseous stream kerogendecomposing heat wave which will thereafter move transversely throughthe shale bed with the assistance of additionally supplied gaseousmaterial to the horizontally moving bed downstream therefrom andeffecting cooling of said kerogen depleted shale With said additionallysupplied gaseous material.

5. In a process for retorting oil shale particulate in a horizontallymoving 'bed wherein heating, thermal decomposition and cooling of shaleparticulate is accomplished with gaseous materials of differenttemperature levels flowing through said bed of shale, the method ofimproving the thermal efficiency of the process for effecting thermaldecomposition of kerogen and recovery of shale oil product whichcomprises recovering separate streams of gasiform material of low,intermediate and higher temperature comprising kerogen decompositionproduct from the bottom of said horizontal moving bed in the directionof shale flow, Without further cooling, separating the low andintermediate temperature gasiform streams into separate gaseous streamsand oil rich streams, using the separated gaseous stream of intermediatetemperature to effect a partial cooling of the highest temperaturegasifor-m material recovered from the shale bed to effect a partialseparation thereof into an oil phase and a relatively high temperaturegaseous stream, condensing additional oil constituents from therelatively high temperature gaseous stream by preheating fresh shaleintroduced to said horizontal moving bed with said high temperaturegaseous stream and employing the lowest temperature gaseous materialrecovered as above recited to cool kerogen depleted shale and generatein an external combustion zone a high temperature kerogen decompositiongas stream which is thereafter passed through the kerogen rich shale bedintermediate the shale preheat step and shale cooling step.

References Cited UNITED STATES PATENTS 7/1931 Trent 202-417 6/1967 Ban208-11 U.S. c1. X.R.

